hosts info config in container

hosts info config in container

JIRA: DOVETAIL-435

in some SUT, there's a need to config hosts <domain name>:<ip> info
in container /etc/hosts, ortherwise, SUT service will not be used.

usage:

1,for dovetail directly running, cd ${DOVETAIL_HOME}/userconfig
  vim hosts.yaml
  sth like
  hosts_info:
    - domain_nameA:192.168.33.101
    - domain_nameB:<some IP>
2,for dovetail container running, first get inside the container,
  cd /home/opnfv/dovetail/userconfig
  vim hosts.yaml
  same as 1.

Change-Id: Ic5d87df3d78c0fa1d08c4e972c0fc97e61b906e9
Signed-off-by: MatthewLi <matthew.lijun@huawei.com>